NAIROBI, Kenya — Somalia’s Islamic extremist rebels killed a Kenyan policeman Thursday when they attacked a police station in northern Mandera County, raising security concerns over next week’s national elections.

Al-Shabab, which is allied to al-Qaida, claimed responsibility for the attack on Lafey police station near the border with Somalia. The group made the claim through its Shahada News Agency’s blog and social media accounts, according to the SITE monitoring group.

Two vehicles were burned in the early morning attack, according to Kenya’s North Eastern regional coordinator Mohamud Saleh.

The violence comes a day after three people died in a suspected al-Shabab attack in southern Kenya and days before Kenya’s national elections on Tuesday.

Al-Shabab has been threatening since March to disrupt the elections and they repeated the threat last week, according to former U.S. Marine and security analyst Andrew Franklin. The attacks come at time when Kenyan security agents are stretched to prevent election violence, Franklin said.

“Without effective security the credibility of the elections cannot be assured,” Franklin said.

Al-Shabab in recent weeks has stepped up deadly attacks in Kenya’s border counties of Lamu and Mandera. Voting will be affected in those areas, said Franklin.

The extremist group has carried out more than 100 attacks inside Kenya, calling it retribution for the East African nation’s deployment of troops to Somalia in 2011 to fight the extremists.